A typical automobile has four wheels and a suspension system wherein the body of the automobile is supported on each wheel by a spring. During a turning maneuver of the automobile, the wheels of the automobile fall into one of two groups—the wheels are either leading wheels or trailing wheels. The leading wheels are the wheels located on the outer radius of the turn and the trailing wheels are the wheels located in the inner radius of the turn.
As an automobile enters a turn, the body of the automobile begins to lean away from the direction of the turn. For example, during a right hand turn, the body of the automobile will lean to the left. Such leaning increases the force acting on the springs of the leading wheels causing them to compress and store energy.
Such leaning has the opposite effect on the springs of the trailing wheels. The leaning of the body towards the leading wheels reduces the weight resting on the springs of the trailing wheels, allowing them to expand and release some or all of the energy that they had been storing, depending upon the dynamics of the turn (i.e., the speed, the angle of direction change, etc.). This release of the energy contributes to the forces already acting on the vehicle, such as centrifugal force, gravity, and other dynamic forces, and can cause the trailing wheels to lift off of the ground (referred to herein as a “wheel lift” event).
In the past, various solutions have been adopted to inhibit the occurrence of a wheel lift event. For example, some automobiles are equipped with a system that is designed to automatically apply the brakes to only some the vehicle's wheels when a dynamic condition is detected that will induce yaw instabilities that can potentially lead to a wheel lift event. Such braking systems apply a yaw-inducing torque to the automobile to counteract certain body motions which, if left unchecked, could potentially cause the trailing wheels to lift. Other automobiles have been equipped with anti-roll bars whose stiffness can be increased automatically when a dynamic condition that will lead to a large body roll is detected. At that time, the stiffness of the anti-roll bars is increased and body lean is diminished. While these solutions are adequate in reducing the yaw instabilities and body roll during a turn event, there is room for improvement in direct roll control of the whole vehicle.